What Are Intestinal Parasites?
Human intestinal parasites are either one-cell organisms or intestinal worms that live in the small or large intestine and use the stool or blood from intestinal wall as a source of food.
One-Cell Parasites – Protozoa
One-cell organisms, like Giardia lamblia, also called Giardia duodenale (Picture 1), Cryptosporidium (crypto) and Cyclospora, utilize nutrients from the stool. They belong to a living kingdom Protozoa (Gk. protos = first; zoa = animals). They may cause inflammation of the small intestine thus hampering absorption of nutrients. Entamoeba hystolytica lives predominantly in the colon.
Picture 1. Parasite giardia from a stool sample,
as seen under the electron microscope (actual size:~0.01 mm)
Intestinal Worms (Helminths)
Intestinal worms (helminths), like roundworms (hookworms, whipworms, Ascaris and Trichinella), tapeworms and flukes, are few millimeters to several meters in size, they eat the bowel content or suck the blood from the intestinal wall and can cause about the same symptoms as one-cell parasites.
How Can One Contract Parasites?
Parasites are shed in human or animal stool; a source of an infection in poor countries is usually stool-contaminated food or water, and in industrialized countries, recreational water (lakes, pools) or homosexual men (1).
Symptoms of Intestinal Parasites
Intestinal parasites can cause one or more of the following symptoms:
- Mild diarrhea with waxing and waning course, appearing few days to several weeks after the travel into the country with poor hygiene, and lasting from several days to months (for comparison: bacterial diarrhea usually has a sudden and dramatic onset within some hours after a meal, and heals on its own in few days).
- Mucus in the bowel movement
- Bloating and flatulence
- Weight loss is common.
- Pale skin, tiredness, tingling (due to reduced absorption of minerals and vitamins).
- Entamoeba histolytica may cause severe colitis with ulcers, abdominal cramps, blood in the stool with occasional pus – the disease is known as amebic dysentery (9). Entamoeba may invade liver, lung, brain, or other organs, where it forms cysts.
- Worms, their parts or eggs can be sometimes found in the stool. Read more about intestinal worms.
- Infection by either one-cell organisms or intestinal worms is often present without any symptoms.
Diagnosis of Intestinal Parasites
Diagnosis can be often suspected from history of prolonged bloating or diarrhea and can be confirmed by the following tests:
- Ova and parasites (O&P) test of the stool. The test is often false negative so three stools from three different days (at least two days apart) should be tested.
- Hemoccult test may reveal blood in the stool
- Blood tests often reveal elevated eosinophils and IgE antibodies and lowered ferritin, hemoglobin or red cells
- CT or biopsy are needed to find cysts in the liver, lungs or brain.
Treatment of Intestinal Parasites
- Anti-parasitic drugs, like metronidazole, quinacrine, tinidazole and furazolidone are usually effective, but the exact treatment regime, as prescribed by your doctor, should be followed. Paramomycin is not absorbed from the intestine into the blood, so it may be used in pregnancy (1). For cyclospora trimethoprim-sulfametoxazol can be used (2).
Intestinal parasites are usually successfully treated, but may reoccur if the source of infection still exists.
Prevention of a Parasitic Infection
An infection by intestinal parasites can be prevented by:
- Hand washing with soap before eating and after bowel movement
- Food cooking kills all parasites (but smoking or freezing does not)
- Washing of raw vegetables and fruits
- Travelers from western countries visiting Central or South America, Africa or South Asia should ingest only packaged, bottled or cooked foods and drinks and only fruits that they can peel by themselves. Read about food disinfection in the article about travelers diarrhea.
For How Long Is a Person with Parasitic Diarrhea Contagious?
The stool of a person with intestinal parasites is contagious as long as infection lasts, or, like in infection with Entamoeba hystolitica, possibly for years after symptoms cessation. The stool of an infected person without any symptoms is also contagious.
- Incidence of intestinal parasites in homosexual men (ncbi.nlm.nih.gov)
- Intestinal protozoa (tulane.edu)